1. Field of the Invention
This invention relates generally to the field of rigid disc drive data storage devices, and more particularly to an improved spindle motor for spinning the discs on which the data is recorded.
2. Brief Description of the Prior Art
Disc drive data storage devices of the type known as "Winchester" disc drives are well known in the industry. Such devices utilize rigid discs coated with a magnetizable medium for the storage of digital information in a plurality of circular concentric tracks, and this information is written to and read from the discs using a data head mounted on an actuator mechanism which moves the head from track to track under control of electronic circuitry. The discs are mounted for rotation on a spindle motor, and as the discs spin, a thin layer of air is dragged along with the discs and forms an "air bearing" on which the heads fly above the surface of the discs. The integrity of this air bearing is dependent, in part on the cleanliness of the air in the vicinity of the heads and disc, and for this reason, the heads and discs are sealed in a housing to prevent the entrance of contaminants and particles.
The earliest 5" Winchester disc drives included a brushless DC spindle motor which was mounted to the base of the housing with the actual motor components outside the housing and the shaft of the motor projecting into the housing, where a hub, fixed to the shaft, was used to mount the discs.
As industry demands for smaller sizes of disc drives lead to the introduction of half-height 5" units, 3", the size and configuration of the spindle motor has also changed, first to the "pancake" spindle motor--which employed an air gap in the motor which was axial in relationship to the motor shaft--and then to the "in-hub" spindle motor--where the motor coils and magnets which make up the motor were located inside the hub which mounted the discs.
The current generation of 2.5" disc drives continues to use this in-hub configuration of spindle motor, but the inner diameter (ID) of the discs in these drives is only 20 mm. This dimension represents about the lower limit for in-hub motors, since the space required for rotor magnets and stator coils of necessary size to start the discs spinning from rest, and the bearings needed to rotate the hub, occupy virtually all available space.
Disc drives in the 1.8" form factor are currently being introduced in which the ID of the discs is only 12 mm. With such a space limitation, there is not sufficient room within the disc-carrying hub for bearings, magnets and coils to ensure adequate starting torque, particularly if the drive configuration includes multiple discs and heads.
A need clearly exists, therefore, for a spindle motor configuration for 1.8" and future smaller disc drives which can provide necessary starting torque, while still minimizing the physical size of the motor to fit within the small mechanical dimensions of such disc drives.